We will study the mechanisms by which virulent and oncogenic viruses replicate, and how this replication affects host cells. Particular emphasis will be placed upon studies concerning the regulation of cellular and viral protein synthesis. In the case of virulent viruses, the mechanisms by which host protein synthesis is shut off, or replaced by viral protein synthesis, will be investigated. Two viruses, reo- and encephalomyocarditis virus, will be compared in this respect. In addition, the effect of pretreatment of the host cell with interferon on viral and host protein synthesis will be studied. In the case of oncornaviruses, regulation of viral and host protein synthesis as a function of cell growth rate will be investigated; again, the effects of interferon pre-treatment on both types of translation will be compared. For reasons of efficiency, convenience and ease of comparisons a single cell line, the murine plasmacytoma MOPC-460, will be used for most of our experiments. This line has already proven very useful for studies in whole cells, in cell-free extracts, and in partially purified protein synthesizing systems. It can be grown in either solid or ascitic form in mice as well as in tissue culture, and supports the efficient replication of reovirus, encephalomyocarditis virus, an AKR-like murine leukemia virus and, in addition, produces large quantities of A-type particles. The relationship of the A-type particles produced by these cells to standard infectious RNA tumor viruses will be further investigated. Comparative studies of A-type particles in murine plasmacytoma and human myeloma cells will also be conducted.